The present invention relates to a drive power transmission device and an image forming apparatus equipped with the drive power transmission device, and in particular, to a drive power transmission device which transmits a rotation drive force coming from a driving source to a detachable driven member, an image forming apparatus equipped with the drive power transmission device and to a process cartridge.
For example, in many image forming apparatuses forming images through an electrophotographic system, a photoreceptor and a developing device are detachably provided on the image forming apparatus main body. As a detachable component to be provided detachably, there are given one wherein a photoreceptor and an individual developing device are unitized integrally, one wherein a photoreceptor and a developing device are united as a unit and common one wherein components around a photoreceptor such as a charging device and a cleaning device in addition to the aforesaid photoreceptor and developing device are formed as a unit to be the detachable component that is called a process cartridge.
The detachable component of this kind includes those which rotate in the course of image forming such as a photoreceptor and a developing sleeve, and these rotary components are connected to a driving source on the image forming apparatus main body then they are mounted.
Incidentally, a drive system that drives rotary components such as a photoreceptor and a developing sleeve is required to be one wherein an occurrence of rotational irregularity and a vibration is strictly repressed. The reason for this is that image quality is easily affected by rotational irregularity and a vibration to the utmost extent. On the other hand, when driving components that can be mounted and dismounted, rotational irregularity and a vibration are easily caused. To satisfy these antinomic requirements, there have been made various inventions.
In TOKKAIHEI 4-15315, there is suggested to use a universal joint wherein rotatable link mechanisms in a plurality of steps are combined.
In JiKKAIHEI 5-25453, TOKKAIHEI 8-6368, TOKKAIHEI 8-6456 and TOKKAIHEI 8-6457, there is described to use a universal joint of a pin-coupling type.
In TOKKAIHEI 8-220938, there is described that a spline-coupling in one step is used. Further, in TOKKAIHEI 9-66637, there is described that a coupling portion is provided on each of an inner circumferential surface and an outer circumferential surface of an elastic member.
In the conventional examples stated above, there is a problem that rotational irregularity and vibration both generated while detachable components are driven to rotate cannot be prevented sufficiently.
It is considered that the causes for occurrence of the rotational irregularity and vibration both generated while detachable components are driven to rotate lie in the following points.
In the drive system wherein connection is cut by dismounting, it is unavoidable to a certain extent that an axis of a driving side is deviated from that of a driven side. Because of this deviation, a deviating force in addition to rotational force is applied to a driven shaft in the course of rotation, and thereby, the rotational irregularity and vibration are caused. Each of a pin type universal joint and a one-step spline coupling is one wherein a driving shaft and a driven shaft are connected with a coupling having a buffer effect to repress an occurrence of rotational irregularity and vibration even when the driving shaft is deviated from the driven shaft, but it has been confirmed that an effect of the repression is not sufficient.
In the conventional technology stated above, therefore, a tolerance for the deviation between the driving shaft and the driven shaft is small, which causes a problem in manufacturing and a cost increase.
Further, since a tolerance for the deviation between the driving shaft and the driven shaft is small, workability for mounting and dismounting is lowered. Further, in the case of a mechanism requiring fixing with a screw for mounting, workability for mounting and dismounting is further lowered. An object of the invention is to solve the problem stated above in the driving system wherein a driven shaft can easily be mounted on a driving shaft.
In accordance with a first aspect of the present invention, an apparatus for forming an image on a recording medium, which has a process cartridge detachably mounted thereto (the process cartridge including at least one element-device, such as a photoreceptor device, an exposure device, a developing device, a charging device and a cleaning device) includes a driving source to generate a rotational-driving force which is transmitted to at least the process cartridge when the process cartridge is mounted on the image apparatus, and a spline joint section to transmit the rotational-driving force from the driving source to the process cartridge when the process cartridge is mounted on the apparatus. The spline joint section includes a first male-spline member which is fitted on a driving axis of the driving source, and an outer surface of which is splined into a plurality of first protrusions. The spline joint section also includes a second male-spline member, which is fitted on a driven axis of the process cartridge, and an outer surface of which is splined into a plurality of second protrusions, and an intermediate female-spline member, a driving side inner surface of which is splined into a plurality of third protrusions while a driven-side inner surface of which is splined into a plurality of fourth protrusions so that the first protrusions of the first male-spline member are engaged with the third protrusions while the second protrusions of the second male-spline member are engaged with the fourth protrusions.
In accordance with another aspect of the present invention, an apparatus for forming an image on a recording medium, which has a process cartridge detachably mounted thereto (the process cartridge including at least one element-device, such as a photoreceptor device, an exposure device, a developing device, a charging device and a cleaning device) includes a driving source to generate a rotational-driving force which is transmitted to at least the process cartridge when the process cartridge is mounted on the apparatus, and a spline joint section to transmit the rotational-driving force from the driving source to the process cartridge when the process cartridge is mounted on the apparatus. The spline joint section includes a first male-spline member, which is fitted on a driving axis of the driving source, and an outer surface of which is splined into a plurality of first protrusions, a second female-spline member which is fitted on a driven axis of the process cartridge, and an inner surface of which is splined into a plurality of second protrusions, and an intermediate spline member, an inner surface of which is splined into a plurality of third protrusions while an outer surface of which is splined into a plurality of fourth protrusions, so that the first protrusions of the first male-spline member are engaged with the third protrusions while the second protrusions of the second female-spline member are engaged with the fourth protrusions.
In accordance with another aspect of the present invention, a spline joint mechanism for transmitting a rotational-driving force generated by a driving source provided in a main apparatus to an objective unit detachably mounted to the main apparatus includes a first male-spline member, which is fitted on a driving axis of the driving source, and an outer surface of which is splined into a plurality of first protrusions, and a second male-spline member which is fitted on a driven axis of the objective unit, and an outer surface of which is splined into a plurality of second protrusions. The spline joint member also includes an intermediate female-spline member, a driving-side inner surface of which is splined into a plurality of third protrusions while a driven-side inner surface of which is splined into a plurality of fourth protrusions, so that the first protrusions of the first male-spline member are engaged with the third protrusions while the second-protrusions of the second male-spline member are engaged with the fourth protrusions. The first male-spline member and the second male-spline member are detachably and loosely engaged with the intermediate female-spline member with movement between them, so as to constitute a universal joint, which can transmit the rotational-driving force from the driving source to the objective unit even if the driving axis does not coincide with the driven axis within a certain range. Each of the first and third protrusions has an affecting surface whose direction coincides with a radial direction of each of the first male-spline member and intermediate female-spline member. When transmitting the rotational-driving force from the first male-spline member to said intermediate female-spline member, affecting surfaces of the first protrusions press-contact affecting surfaces of the third protrusions, so that a component force of the rotational driving force is not generated in a direction other than that orthogonal to the affecting surface.
In accordance with another aspect of the present invention, a spline joint mechanism for transmitting a rotational-driving force, generated by a driving source provided in a main apparatus, to an objective unit detachably mounted to the main apparatus, includes a first male-spline member, which is fitted on a driving axis of the driving source, and an outer surface of which is splined into a plurality of first protrusions, a second female-spline member which is fitted on a driven axis of the objective unit, and an outer surface of which is splined into a plurality of second protrusions. The spline joint mechanism also includes an intermediate spline member, an inner surface of which is splined into a plurality of third protrusions while an outer surface of which is splined into a plurality of fourth protrusions, so that the first protrusions of the first male-spline member are engaged with the third protrusions while the second protrusions of the second female-spline member are engaged with the fourth protrusions. The first male-spline member and the second female-spline member are detachably and loosely engaged with the intermediate spline member with movement therebetween so as to constitute a universal joint which can transmit the rotational-driving force from the driving source to the objective unit even if the driving axis does not coincide with the driven axis within a certain range. Each of the first and third protrusions has an affecting surface whose direction coincides with a radial direction of each of the first male-spline member and intermediate spline member, and when transmitting the rotational-driving force from the first male-spline member to the intermediate spline member, affecting surfaces of the first protrusions press-contact affecting surfaces of the third protrusions, so that a component force of the rotational-driving force is not generated in a direction other than that orthogonal to the affecting surface.